Gesneriaceae

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Introduction

The Gesneriaceae are a mid-sized to large plant family comprising
approximately 2500-3500 species in 120-135 genera, distributed
primarily in the tropics with a few temperate species in Europe, China and Japan. The majority of species are herbaceous perennials, but they also can be annuals, shrubs, lianas, and trees. Many species (20%) are epiphytic, and the Gesneriaceae ranks among the top ten plant families in terms of absolute numbers of epiphytic taxa.

The Gesneriaceae are often referred to as tropical Scrophulariaceae and are closely related to this plant family. They are also closely related to Bignoniaceae and Acanthaceae but are distinguished from these families by the combination of five-lobed corollas, parietal placentation, and presence of endosperm in most species.

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Figure 1. Cyrtandra hawaiiensis X Cyrtandra calpidicarpa from Hawai'i. The Hawaiian species of Cyrtandra represent an intriguing evolutionary story in that all 54 species are found only on the Hawaiian islands and have resulted in 75 interspecific, naturally occurring hybrids.

The Gesneriaceae are primarily a tropical family found in both New and
Old World tropics, although there are some temperate representatives in
Europe and Asia. For the most part, the subfamily Gesnerioideae is found
in the New World, the exceptions being members of the tribe
Coronanthereae which are also found in Australia and the South Pacific.
Cyrtandroideae are restricted to the Old World. Members of the tribe Klugieae, which has traditionally been placed within the subfamily Cyrtandroideae, are also found exclusively in the Old world, the one exception being Rhynchoglossum azureum from Central America.

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Figure 2. Cyrtandra oxybapha from Hawai'i, a representative of the
Cyrtandroideae.

Characteristics

Leaves are opposite in the majority of the Gesneriaceae but in many
species anisophylly where the leaves are unequal in size occurs. This is sometimes so extreme that the smaller leaf is either inconspicuous or even falls off early creating an alternate leaf arrangement. Members of the Gesneriaceae have 5-lobed corollas with fused petals. In the majority of species these corollas are long and tubular, however in some the corolla tube is shortened and flattened. The shorter corolla tube is found in the most widely known and cultivated member of this family, the African violet (Saintpaulia).

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Figure 4. Columnea densibracteata from Ecuador. The brightly colored undersides of the leaves are believed to act as an additional signal to attract pollinators to the contrasting yellow flowers.

Another interesting feature of the Gesneriaceae is that the cotyledons do not expand equally upon germination in nearly all members of the subfamily Cyrtandroideae. In most instances the plant will develop normally, but in Streptocarpus and Monophyllaea, the single cotyedon may become the entire vegetative portion of the plant with flower stalks arising from the cotyledon (Figure 3).

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Figure 3. Unequal cotyledon expansion becomes extreme in some members of the Gesneriaceae as shown here with Streptocarpus. The cotyledon is the entire vegetative portion of the plant.

Discussion of Phylogenetic Relationships

Classifications of the Gesneriaceae traditionally recognize two
subfamilies (Gesnerioideae and Cyrtandroideae). The division of the
family is largely based on the uniform (Gesnerioideae), or uneven
(Cyrtandroideae) enlargement of the cotyledons after germination (Burtt,1962). Another character that has been useful in separating the subfamilies is the presence (Gesnerioideae) or absence (Cyrtandroideae) of endosperm in the seed. The two subfamilies have been divided further into 9-17 tribes. The tree presented here is based on a cladistic analysis of DNA sequences. The aim of this work was to resolve more clearly the phylogenetic relationships among taxa and to propose a more stable classification scheme. The two subfamilies have been identified as monophyletic and the tribe Klugieae (Cyrtandroideae) appears to be separate and sister to the remainder of the family.

The traditionally recognized tribes Trichosporeae and Didymocarpeae are not monophyletic in this analysis and are represented here by several different lineages. The Trichosporeae are monophyletic in
an analysis of morphological data whereas the Didymocarpeae were also
polyphyletic (Smith 1996). These two tribes will need further investigation although the Didymocarpeae is such a large heterogenous group that dividing it into smaller groups is probably the best solution.

The relationships presented here are comparable to studies based on
morphological data (Smith 1996), the main exception being that the subfamily
Cyrtandroideae was found to be paraphyletic. The Klugieae were also
found to be the sister to the remainder of the family in this analysis.
A combined analysis of morphology, ndhF gene sequences and rbcL gene
sequences differs in the placement of the Klugieae, however; rather than being the sister of the remainder of the family, this group is in its traditional place as a member of the Cyrtandroideae.

About This Page

Page: Tree of Life
Gesneriaceae.
Authored by
James F. Smith.
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First online 20 April 1998

Citing this page:

Smith, James F.
1998. Gesneriaceae.
Version 20 April 1998. http://tolweb.org/Gesneriaceae/20861/1998.04.20in The Tree of Life Web Project, http://tolweb.org/

Each ToL branch page provides a synopsis of the characteristics of
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